KR20030044822A - Light guiding plate for front light - Google Patents

Abstract

PURPOSE: To provide a light guide plate for a front light which has improved luminance and uniformized luminance distribution while maintaining visibility by reducing parallax in a substantially unrecognizable state. CONSTITUTION: The light guide plate 14 receives the light of a light source 15 from the incident plane 14a of a side face, and emits the light from a light- emitting plane 14c opposed to a liquid crystal panel 12. The light guide plate 14 is formed so that a tilting angle θ formed by a straight line passing through a position at the opposite side end part of the light-emitting plane 14c in the incident plane 14a and a position at the opposite side end part of the light- emitting plane 14c in an opposite plane 14b opposed to the incident plane 14a of the light guide plate 14, and the light-emitting plane 14c become 0.2°<θ<0.75°. A large number of grooves 17 are formed on a plane 14d opposed to the light- guide plane 14c for reflecting light incident from the incident plane 14a in an emission direction from the light-emitting plane 14c. An inclined plane 17a which inclines upward toward the opposite plane 14b from the incident plane 14a, and an light collecting plane 17b which is inclined downward from the incident plane 14a toward the opposite plane 14b are formed at the grooves 17 so as to alternately be continued.

Description

Light guide plate for front light {LIGHT GUIDING PLATE FOR FRONT LIGHT}

The present invention relates to a light guide plate for a front light mounted on a reflective display device.

In order to reduce power consumption, a conventional display device has a front light. When the external brightness is sufficient, this type of display device uses external light such as sunlight and room light. If the external brightness is not sufficient, the display device uses the front light. Such displays include reflective displays with front lights.

FIG. 5A shows a conventional reflective liquid crystal display 51 with a front light 53. As shown in FIG. The display device 51 includes a reflective liquid crystal panel 52. The front light 53 faces the liquid crystal panel 52. The front light 53 includes a light guide plate 54 and a light source 55 facing one end (incident surface) 54a of the light guide plate 54. The thickness of the light guide plate 54 is substantially uniform. The emission surface 54b of the light guide plate 54 faces the liquid crystal panel 52. On the reflection-emitting surface 54d opposite to the emission surface 54b, a groove (not shown) is formed so as to reflect light from the light source 55 to the emission surface 54b. Light emitted from the light source 55 and incident on the light guide plate 54 through the incident surface 54a is guided through the light guide plate 54 during total reflection and is irradiated onto the liquid crystal panel 52 through the exit surface 54b. do.

FIG. 5B shows another conventional reflective liquid crystal display device 151. As shown in FIG. The display device 151 includes a wedge-shaped light guide plate 154. The thickness of the light guide plate 154 decreases from the incident surface 154a toward the opposite end surface 154c. The structure of the display device 151 other than the light guide plate 154 is the display device 51 of FIG. Is the same as

In order to improve the visibility of the liquid crystal panel 52, the light guide plates 54 and 154 are designed to ensure luminance. Compared to the flat light guide plate 54 shown in FIG. 5 (a), light incident on the wedge light guide plate 154 leaks less through the opposite end face 54 c facing the incident surface 54 a. do. Compared to the flat light guide plate 54, the wedge light guide plate 154 has a more uniform brightness (see Japanese Patent Application Laid-Open No. 11-242220).

The brightness of the flat light guide plate 54 is improved by deepening the grooves. However, if the depth of the groove is excessive, the groove itself is visible, which lowers the visibility of the display device. On the other hand, the wedge-shaped light guide plate 154 easily improves the brightness as compared with the planar light guide plate 54. However, if the thickness of the light guide plate 154 at the incident surface 54a and the thickness at the opposite surface 54c are significantly different, that is, the angle θ defined by the reflection-emitting surface 54d and the emission surface 54b is If large, parallax occurs, resulting in a double phase. The light beam L1 incident on the light guide plate 154 and exited through the emission surface 54b is reflected by the liquid crystal panel 52, re-entered into the light guide plate 154, and exits through the reflection-emitting surface 54d. Part of the light beam L1 is reflected back by the reflection-emitting surface 54d. The re-reflected portion of the light beam L1 is reflected back by the emission surface 54b to exit the light guide plate 154 through the reflection-emitting surface 54d. This part of the ray L1 is represented by L2 in FIG. 6. As a result, the dual phase appears on the display device 52.

If the inclination angle θ is not appropriate, the luminance will not be uniform. That is, uniform luminance cannot be obtained. Japanese Patent Laid-Open No. 11-242220 discloses a wedge-shaped light guide plate for improving the uniformity of luminance. However, this publication does not disclose the relationship between the inclination angle θ and the uniform luminance distribution with respect to parallax.

Accordingly, an object of the present invention is to provide a light guide plate for a front light which minimizes the parallax to an unrecognizable level, thereby improving visibility and improving uniformity of luminance distribution.

In order to achieve the above and other objects according to the object of the present invention, the present invention provides a light guide plate for a front light mounted on a reflective display device having a display portion. The light guide plate guides light from a light source and irradiates the light onto a display unit. The light guide plate has an entrance surface, an opposite end surface, an exit surface facing the display portion, and a reflection-emitting surface. The incident surface causes light to enter the light guide plate. The opposite end face faces the incident face. Light incident on the light guide plate through the incident surface exits toward the display through the emission surface. The reflection-emitting surface faces the emission surface. The light reflected on the display portion passes through the emission surface and the reflection-emission surface. The reflection-emitting surface has a first end that intersects the incident surface and a second end that intersects the opposite end surface. The inclination angle formed by the line including the first end and the second end and the incident surface is larger than 0.2 ° and smaller than 0.75 °. The reflection-emitting surface includes a light portion that reflects light incident on or incident on the incident surface to the exit surface.

Fig. 1A is a schematic side view showing a liquid crystal display device according to a first embodiment of the present invention.

FIG. 1B is a partially enlarged view of the device of FIG. 1A.

2 is a schematic side view illustrating a light guide plate according to another embodiment of the present invention.

3 is a graph showing the relationship between the luminance uniformity and the incident angle [theta].

4 is a graph showing the relationship between the luminance and the incident angle [theta].

5 (a) and 5 (b) are schematic side views illustrating a conventional light guide plate.

6 is a partially schematic view showing the mechanism of a dual phase.

[Explanation of symbols on the main parts of the drawings]

11 Reflective Liquid Crystal Display 12 LCD Panel

13 front light 14 light guide plate

15 Light Source 16 Reflector

17 home

Referring to Figs. 1 (a) and 1 (b), a reflective liquid crystal display device 11 according to an example of the present invention will be described. FIG. 1A is a schematic diagram showing the arrangement of the liquid crystal panel 12 and the front light 12 of the display device 11. FIG. 1B is a partially enlarged view of FIG. 1A.

As shown in FIG. 1A, the display device 11 includes a display portion and a front light 13. In this embodiment, the display portion is a liquid crystal panel 12. The front light 13 covers the front surface of the liquid crystal panel 12 (upper side in Fig. 1 (a)). The front light 13 includes a light guide plate 14, a light source 15, and a reflector 16. The light guide plate 14 guides light to the liquid crystal panel 12. The reflector 16 reflects light from the light source 15 toward the light guide plate 14.

As the light source 15, for example, a cold cathode tube (fluorescent tube) is used. The light guide plate 14 is made of a material having high transparency, for example, a rectangular acrylic plate. The light guide plate 14 is substantially wedge shaped. The light guide plate 14 has an incident surface 14a opposite the light source 15, and an opposite end surface 14b located on the opposite side of the incident surface 14a. The length d1 of the incident surface 14a is longer than the length d2 of the opposite end surface 14b. That is, the thickness of the light guide plate 14 gradually decreases from the incident surface 14a toward the opposite end surface 14b. The incident surface 14a extends in the direction perpendicular to the surface of the drawing. The exit surface 14c of the light guide plate 14, which faces the liquid crystal panel 12, is perpendicular to the incident surface 14a. One end of the reflection-emitting surface 14d that intersects the incident surface 14a is regarded as the first end. The other end of the reflection-emitting surface 14d that intersects the opposite end surface 14b is considered the second end. The inclination angle θ defined by the line including the first end and the second end and the exit surface 14c is in the range of 0.2 ° <θ <0.75 °.

As shown in Fig. 1 (b), a plurality of grooves 17 are formed on the reflection-emitting surface 14d opposite to the exit surface 14c. The groove 17 reflects light incident on the light guide plate through the incident surface 14a and guides the light from the incident surface 14a to the exit surface 14c. Each groove 17 extends in parallel with the incident surface 14a. Each groove 17 has a first inclined surface 17a and a second inclined surface 17b. The second inclined surface 17b serves as a light mining surface. The first inclined surface 17a is inclined such that the distance between the exit surface 14c and the reflection-emitting surface 14d increases from an end closer to the incident surface 14a to an end closer to the opposite end surface 14b. Lose. The second inclined surface 17b is inclined such that the distance between the exit surface 14c and the reflection-emitting surface 14d decreases from an end closer to the incident surface 14a to an end closer to the opposite end surface 14b. Lose. The first inclined surface 17a and the second inclined surface 17b are alternately arranged. In other words, in this embodiment, the groove 17 has a sawtooth cross section.

The angle of the second inclined surface 17b is an angle close to the perpendicular to the emission surface 14c for light in which each second inclined surface 17b is incident or reflected toward the exit surface 14c toward the exit surface 14c. Is determined to reflect both. Angle (alpha) defined by the surface parallel to the 1st inclined surface 17a and the emission surface 14c is set to 1 degree and 5 degree range, for example. Angle (beta) defined by the plane parallel to the 2nd inclined surface 17b and the exit surface 14c is set to 41 degrees and 47 degrees, for example.

The pitch P of the grooves 17 is set equal to the pixel pitch of the liquid crystal panel 12, for example. As shown in FIG. 1B, the pitch P of the grooves 17 is regarded as the distance between the bottom of one of the grooves 17 and the bottom of the adjacent groove 17. The depth of the groove 17 increases as the distance from the incident surface 14a increases. In this embodiment, the bottoms of the grooves 17 are arranged at equal intervals.

The pitch of the grooves 17 is actually 1 mm or less and the number of the grooves 17 is quite large. However, in Fig. 1 (a) the groove 17 is not shown. In Fig. 1 (b) a small number of grooves 17 are shown roughly. For ease of illustration, the ratio of the light source 15, the light guide plate 14, and the liquid crystal panel 12 is different in Figs. 1 (a) and 1 (b).

The operation of the display device 11 will now be described. When the outside is sufficiently bright, the display device 11 uses sunlight or room light, for example. When the outside is not bright enough, the display device 11 uses the light source 15. External light enters the light guide plate 14 through the reflection-emitting surface 14d. The external light then exits the light guide plate 14 through the exit surface 14c and is irradiated onto the liquid crystal panel 12.

When the light source 15 is used, light is advanced through the light guide plate 14 as shown in FIG. 1 (b). The light reaching each second inclined surface 17b is reflected at an angle close to the perpendicular to the exit surface 14c and exits through the exit surface 14c. Light irradiated onto the liquid crystal panel 12 is reflected by the liquid crystal panel 12 and reincident to the light guide plate 14. The light transmitted through the light guide plate 14 then exits the light guide plate 14 through the reflection-emitting surface 14d, and the light is visible.

In the macroscopic view, the thickness of the light guide plate 14 decreases from the incident surface 14a toward the opposite end surface 14b. Therefore, as compared with a flat light guide plate having a uniform thickness, there is less ratio of light incident on the light guide plate 14 through the incident surface 14a and exiting the light guide plate 14 through the opposite end surface 14b. As the distance from the light source 15 increases, the ratio of the depth of the grooves 17 to the thickness of the light guide plate 14 increases. Thus, even when the groove 17 is relatively low, the luminance of the display device 11 increases. Even when the depth of the groove 17 formed in the reflection-emitting surface 14d is set lower than in the case of the light guide plate having a uniform thickness, a sufficient amount of luminance is obtained. As the inclination angle θ increases, the luminance increases. However, in the case where the inclination angle θ is excessive, the luminance of the region far from the light source 15 will increase excessively and the luminance will be uneven. Therefore, there is a suitable range of the inclination angle θ.

Luminance uniformity is an indicator of luminance distribution. Luminance uniformity is calculated in the following manner. First, the surface of the light guide plate 14 is divided into 16 sections by three parallel lines and the other three vertical lines perpendicular to the three parallel lines. Luminance is measured at each of the nine intersections, dividing the minimum value of luminance by the maximum value, and the result represents luminance uniformity. The closer the value is to 1, the smaller the difference between the minimum and maximum values of luminance, i.e., the more uniform the luminance distribution.

The inventors studied the appropriate range of the inclination angle θ, and FIGS. 3 and 4 show the results of this study. 3 shows the relationship between the luminance uniformity and the inclination angle θ, where the luminance uniformity is set as 1 when the inclination angle θ is 0.4 °. 4 shows the relationship between the luminance and the tilt angle θ, where the luminance is set as 1 when the tilt angle θ is 0.4 °.

As shown in FIG. 3, the luminance uniformity has a maximum value with respect to the inclination angle θ. Therefore, there exists an optimal tilt angle θ with a uniform luminance distribution. As shown in Fig. 4, the luminance increases as the inclination angle θ increases. By setting the range of the inclination angle θ that satisfies the inequality 0.2 ° <θ <0.75 °, the luminance is increased while ensuring the uniformity of the luminance distribution. In particular, when the inclination angle θ is 0.4 ° (θ = 0.4 °), the luminance uniformity is maximum, and the uniformity of the luminance distribution is optimal. The uniformity of the luminance in the case of satisfying the inequality 0.2 ° <θ <0.75 ° is 85% of the luminance uniformity when the inclination angle θ is 0.4 ° and is sufficient for practical use. The luminance uniformity when the range of the inclination angle θ is set to satisfy the inequality 0.3 ° <θ <0.6 ° is 93% of the luminance uniformity when the inclination angle θ is 0.4 °. Therefore, the luminance becomes more uniform.

Samples of the light guide plate 14 were prepared. The sample is a wedge having a length of 65 mm, a width of 80 mm, a maximum thickness (d1) of 1 mm, a minimum thickness of (d2) of 0.7 mm, a pitch of P (0.2) of 4 mm, a groove depth of 5.5 to 11 μm, and an inclination angle (β) of 44 °. It is a light guide plate. Other samples identical to the first sample were also prepared except that the thickness was 1 mm. The luminance and luminance uniformity of the two samples were tested. When the brightness of the wedge-shaped light guide plate 14 was set to 1, the brightness of the flat light guide plate was 0.76. That is, the wedge-shaped light guide plate 14 has a considerably improved brightness. When the luminance uniformity of the wedge-shaped light guide plate 14 was set to 1, the luminance uniformity of the flat plate-shaped light guide plate was 0.68. That is, the wedge-shaped light guide plate has significantly improved brightness uniformity. In addition, it was confirmed that the parallax of the wedge-shaped light guide plate 14 was minimized to an unrecognizable degree. This improves visibility.

This embodiment provides the following advantages.

(1) From the macroscopic point of view, the light guide plate 14 is formed in a wedge shape, and its thickness is gradually reduced from the incident surface 14a to the opposite side surface 14b. Therefore, even when the depth of the groove 17 formed in the reflection-emitting surface 14d is set lower than that of the light guide plate having a uniform thickness, a sufficient amount of luminance is obtained even if the hole 17 itself is not visible.

(2) The inclination angle θ defined by the line including the first and second ends of the reflection-emitting surface 14d and the emission surface 14c is greater than 0.2 ° and smaller than 0.75 °. Therefore, the parallax is minimized to the extent that the parallax is not recognized, thereby improving the visibility of the display device 11. This improves luminance and luminance uniformity.

(3) The pitch P of the grooves 17 is set to be the same as the pixel pitch of the liquid crystal panel 12, and the interference pattern cannot be seen.

(4) The distance between the point where the inclined surfaces 17a and 17b of each groove 17 intersect and the exit surface 14c decreases from the incident surface 14a side toward the opposite end surface 14b. The amount of light reaching the area far from the light source 15 is less than the amount of light reaching the area close to the light source 15. However, due to the shape of the groove 17, the area of the second inclined surface 17b is large in the area far from the light source 15. Therefore, a relatively large amount of light is reflected and guided to the exit surface 14c at an angle close to the exit surface 14c. Therefore, sufficient luminance and luminance uniformity are ensured in a region far from the light source 15 without changing the thickness of the light guide plate 14 to the extent that parallax occurs.

It will be apparent to one skilled in the art that the present invention may be practiced in other specific forms without departing from the spirit and scope of the invention. In particular, it should be understood that the present invention can be implemented in the following forms.

Instead of the serrated groove on the light guide plate 14, a groove 18 having a V-shaped cross section can be formed as the light receiving portion as shown in FIG. Each groove 18 is defined by a first inclined surface 18b and a second inclined surface 18a. The inclined surfaces 18b and 18a function as light mining surfaces. In each groove 18, the second inclined surface 18a near the incident surface 14a reflects all the light incident through or incident on the incident surface 14a and toward the exit surface 14c. To guide. The reflected light advances in a direction substantially perpendicular to the exit surface 14c and passes through the exit surface 14c. In each groove 18, the first inclined surface 18b further away from the incidence surface 14a reflects all the light reflected by the opposite end surface 14b and directs the light toward the exit surface 14c. . The reflected light advances in a direction substantially perpendicular to the exit surface 14c and passes through the exit surface 14c. Thus, the light reflected by the opposite end face 14b is used. That is, light incident on the light guide plate 14 is effectively emitted from the emission surface 14c to improve the brightness.

The angle defined by the second inclined surface 18a and the exit surface 14c may be different from the angle defined by the first inclined surface 18b and the exit surface 14c.

As shown in FIG. 2, a reflector 19 may be located on the opposite end surface 14b of the light guide plate 14 to reflect light reaching the opposite end surface 14b. The reflector 19 can be formed by depositing aluminum or silver on the opposite end face 14b. Alternatively, the reflector 19 may be formed by attaching a reflecting film (for example, a white polyester film) on the opposite end surface 14b. Since the reflecting mirror 19 prevents light from exiting from the opposite end surface 14b, light incident on the light guide plate 14 is effectively used. The advantage of the reflector 19 is more manifested in the structure of the groove 18 having a V-shaped cross section.

Instead of forming a reflecting mirror in the light guide plate 14, a reflecting surface can be formed at a position opposite to the opposite end surface 14b of the wall of the housing that accommodates the light guide plate 14.

The antireflection treatment can be applied to the exit surface 14c of the light guide plate 14. This antireflection treatment can be carried out by a conventional method such as adhesion of a film, vacuum deposition, dip method, or thermal transfer method. This antireflection treatment improves the visibility of the image on the liquid crystal panel 12.

Inorganic glass may be used instead of a transparent resin such as acrylic, but it is preferable to use a transparent resin to reduce weight and improve processability.

The size of the light guide plate 14 is not limited to the above-described embodiment. In particular, the light guide plate 14 is formed to have a size corresponding to the size of the corresponding display device (1 to 10 inches diagonally).

Instead of the grooves 17 or 18 serving as the light mining portion, a plurality of points or recesses may be formed in the exit surface 14c and the reflection-emitting surface 14d. In this case, the point and the recess have a triangular cross section.

The light source 15 is not limited to a cold cathode tube. A fluorescent tube such as a hot cathode tube or a light emitting diode (LED) may be used. Alternatively, the linear light source disclosed in Japanese Patent Laid-Open No. 2000-11723 can be used. This linear light source is provided with point light sources, such as LED, and the light guide body which converts the light from a light source into linear light.

Instead of inclining the reflection-emitting surface 14d, the emitting surface 14c can be inclined. In this case, the reflective exit face 14d is parallel to the liquid crystal panel 12, and the incident face 14a is substantially perpendicular to the reflection exit face 14d. The exit surface 14c is inclined so as to approach the exit surface 14c with the reflection- exit surface 14d from the surface side opposite the light source 15 to the opposite end surface 14b side.

Accordingly, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of equivalents of the appended claims.

According to the present invention described above, the parallax can be minimized to an unrecognizable degree, thereby improving visibility and improving uniformity of the luminance distribution.

Claims (10)

A light guide plate for front light mounted to a reflective display device having a display portion 12, wherein the light guide plate guides light from the light source 15 and irradiates the light to the display portion 12, wherein the light guide plate is configured to emit light. An incidence surface 14a incident on the light guide plate, an opposite end surface 14b located opposite the incidence surface 14a, and an exit surface 14c opposite to the display portion 12; In the light guide plate in which light incident on the light guide plate through the light exits from the exit surface 14c toward the display unit 12, The light guide plate has a reflection-emitting surface 14d positioned opposite to the emission surface 14c, and the light reflected from the display portion 12 passes through the emission surface 14c and the reflection-emitting surface 14d. The reflection-emitting surface 14d has a first end that intersects the incidence surface 14a and a second end that intersects the opposite end surface 14b, the line comprising the first end and the second end; The inclination angle formed by the incident surface 14a is larger than 0.2 ° and smaller than 0.75 °, and the reflection-emitting surface 14d is incident through the incident surface 14a or reflected on the incident surface 14a. A light guide plate for front light, characterized in that it comprises a light guide portion for reflecting light on the exit surface (14c). 2. The groove according to claim 1, wherein a plurality of grooves (17) having a sawtooth-shaped cross section are formed on the reflection-emitting surface (14d), each groove 17 having a first inclined surface 17a and a second inclined surface. The light guide plate for front lights formed from 17b, and this 2nd inclined surface 17b acts as a light receiving part. 3. The second inclined surface 17b according to claim 2, characterized in that each second inclined surface 17b is inclined such that the distance between the second inclined surface 17b and the exit surface 14c is reduced toward the opposite end surface 14b. Light guide plate for front light. The light guide plate according to claim 2, characterized in that the groove (17) extends parallel to the incident surface (14a). 2. A plurality of grooves 18 are formed on the reflection-emitting surface 14d, each having a V-shaped cross section, each groove 18 having a first slope 18b and a second slope. A light guide plate for front light, characterized in that it is formed of (18a), and these inclined surfaces (18b, 18a) act as light guides. 6. The light guide plate according to claim 5, wherein the groove (18) extends parallel to the incident surface (14a). 6. A reflector (19) is formed on the opposite end surface (14b), characterized in that the reflector (19) reflects light incident on the light guide plate through the incident surface (14a). Light guide plate for front light. 8. The first inclined plane 18b according to claim 7, wherein each first inclined plane 18b reflects the light reflected by the reflector 19 toward the exit plane 14c, and each second inclined plane 18a is an incidence plane 14a. A light guide plate for front light, characterized in that the light incident through or reflected on the incident surface (14a) is reflected toward the exit surface (14c). 3. The distance between the line where each first inclined surface 17a intersects the corresponding second inclined surface 17b and the exit surface 14c is reduced toward the opposite end surface 14b. Light guide plate for front light. 10. The light guide plate according to any one of claims 1 to 9, wherein at least one of the emission surface (14c) and the reflection-emitting surface (14d) is subjected to an anti-reflection treatment.